First you have to set baud rate of 57600 bps to communicate with r303 fingerprint module. Then you have to send command like Get Image, Generate char file from image, Generate template & store template from the microcontroller.
After giving any command from the controller the r303 module will acknowledge that command & you have to check confirmation code from that acknowledgement.
Read the the datasheet & try the code coming with cd of r303 fingerprint module.